$ { \left[\begin{array}{rr}{-1} & {0} \\ {1} & {1}\end{array}\right]+\left[\begin{array}{rr}{3} & {1} \\ {1} & {-1}\end{array}\right] = {?} } $
Explanation: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rr}{-1}+{3} & {0}+{1} \\ {1}+{1} & {1}+{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{2} & {1} \\ {2} & {0}\end{array}\right]}$